In a modern development of a new medicine, it is necessary to early ascertain toxicity caused by a drug. As one of the toxicities, drug induced (acquired) long QT syndrome, which is a disease causing serious arrhythmia for a patient is known.
The drug induced QT syndrome is a serious disease in which a QT interval is extended in an electrocardiogram after the administration of a drug, causing TdP (Torsades de pointes, Torsades de pointes is a nonsustained polymorphic ventricular tachycardia) and some occurrence of ventricular fibrillation leading to syncope or sudden death. Actually, out of 25 items of drugs which sales were discontinued in the market of the United States since 1980, 5 items of the drugs were confirmed as doubtful that the drugs might provoke the drug induced QT syndrome.
In this manner, many drugs, which are developed as new drug candidates, drop out at clinical or preclinical stages due to the revealing of their toxicity, and that is a big problem. Therefore, in order to ascertain the toxicity caused by a drug, various test to measure membrane potential have been made by penetrating a cell membrane to insert an electrode into a cell. In this kind of drug test, inspecting the toxicity of the drug at an early stage is required.
As a method for obtaining the test result earlier, an influence of an activity of an ion channel by a drug is observed by a change of a cellular potential of the cell in a culture medium, which the drug is added. In the following non-patent reference 1, a well plate to be used for the test method is disclosed.
The well plate is provided with a plurality of wells, which is opened at an upper face, and each well is for congaing cells with culture medium. At a bottom of each well is formed in a flat manner and is disposed a measuring electrode and a grounded reference electrode.
When a cell is in touch with the measuring electrode in the well, extracellular potential of cells changing by an activity of an ion channel is applied to the measuring electrode, and it causes a potential difference between the measuring electrode and reference electrode. By measuring a change in the potential difference between the both electrodes before and after the adding of the drug, an influence of a drug to a cell is observed.
Non-patent reference 1: Bioresearch Center Co., “QT screen”, [online], [Aug. 27, 2007], Internet <URL: http//www.brck.co.JP/MCS/qtscreencataloguejpl.pdf>